What is the primary effect of Duverger's Law?

Duverger's Law posits that in electoral systems that utilize single-member districts and plurality voting (often referred to as "first-past-the-post"), there will typically be a tendency toward a two-party system. This phenomenon occurs because, in such electoral environments, voters often feel compelled to support one of the two leading parties to avoid "wasting" their votes on candidates from smaller parties that are unlikely to win.

As a result, smaller parties struggle to gain significant traction in elections, leading to a political landscape dominated by two major parties that can effectively garner the majority of voter support. This consolidation is further influenced by strategic voting, where individuals choose between the two largest parties rather than voting for a third party that may align more closely with their preferences but lacks the viability to win.

In summary, the primary effect of Duverger's Law is the emergence of a two-party system in electoral systems characterized by single-member districts. This explains why the selected answer is correct, as this law succinctly captures the relationship between electoral mechanics and party systems within a given political framework.